org.chocosolver.solver.constraints.ternary.PropXplusYeqZ Maven / Gradle / Ivy
/*
* This file is part of choco-solver, http://choco-solver.org/
*
* Copyright (c) 2020, IMT Atlantique. All rights reserved.
*
* Licensed under the BSD 4-clause license.
*
* See LICENSE file in the project root for full license information.
*/
package org.chocosolver.solver.constraints.ternary;
import org.chocosolver.solver.constraints.Propagator;
import org.chocosolver.solver.constraints.PropagatorPriority;
import org.chocosolver.solver.exception.ContradictionException;
import org.chocosolver.solver.learn.ExplanationForSignedClause;
import org.chocosolver.solver.variables.IntVar;
import org.chocosolver.solver.variables.events.IntEventType;
import org.chocosolver.util.ESat;
import org.chocosolver.util.objects.setDataStructures.iterable.IntIterableRangeSet;
import org.chocosolver.util.objects.setDataStructures.iterable.IntIterableSetUtils;
/**
* A propagator to ensure that X + Y = Z holds, where X, Y and Z are IntVar.
* This propagator ensures AC when all variables are enumerated, BC otherwise.
*
* Project: choco.
* @author Charles Prud'homme
* @since 03/02/2016.
*/
public class PropXplusYeqZ extends Propagator {
/**
* Position of X in {@link #vars}
*/
private final int x = 0;
/**
* Position of Y in {@link #vars}
*/
private final int y = 1;
/**
* Position of Z in {@link #vars}
*/
private final int z = 2;
/**
* Set to true if X, Y and Z are bounded
*/
private final boolean allbounded;
/**
* Temporary structure to ease filtering
*/
private final IntIterableRangeSet r1;
private final IntIterableRangeSet r2;
private final IntIterableRangeSet r3;
/**
* Create propagator for ternary sum: X + Y =Z
* @param X an integer variable
* @param Y an integer variable
* @param Z an integer variable
*/
public PropXplusYeqZ(IntVar X, IntVar Y, IntVar Z) {
super(new IntVar[]{X, Y, Z}, PropagatorPriority.TERNARY, false);
allbounded = (!X.hasEnumeratedDomain() & !Y.hasEnumeratedDomain() & !Z.hasEnumeratedDomain());
r1 = new IntIterableRangeSet();
r2 = new IntIterableRangeSet();
r3 = new IntIterableRangeSet();
}
@Override
public void propagate(int evtmask) throws ContradictionException {
/*while */
boolean loop;
do {
loop = filterPlus(z, x, y);
loop |= filterMinus(x, z, y);
loop |= filterMinus(y, z, x);
loop &= allbounded; // loop only when BC is selected
} while (loop);
}
/**
* Remove from vars[vr] holes resulting of vars[v1] + vars[v2]
* @param vr position of in vars
* @param v1 position of in vars
* @param v2 position of in vars
* @return true if vars[vr] has changed
* @throws ContradictionException if failure occurs
*/
private boolean filterPlus(int vr, int v1, int v2) throws ContradictionException {
int lb = vars[v1].getLB() + vars[v2].getLB();
int ub = vars[v1].getUB() + vars[v2].getUB();
boolean change = vars[vr].updateBounds(lb, ub, this);
if (!allbounded) {
r1.copyFrom(vars[v1]);
r2.copyFrom(vars[v2]);
IntIterableSetUtils.plus(r3, r1, r2);
change |= vars[vr].removeAllValuesBut(r3, this);
}
return change;
}
/**
* Remove from vars[vr] holes resulting of vars[v1] - vars[v2]
* @param vr position of in vars
* @param v1 position of in vars
* @param v2 position of in vars
* @return true if vars[vr] has changed
* @throws ContradictionException if failure occurs
*/
private boolean filterMinus(int vr, int v1, int v2) throws ContradictionException {
int lb = vars[v1].getLB() - vars[v2].getUB();
int ub = vars[v1].getUB() - vars[v2].getLB();
boolean change = vars[vr].updateBounds(lb, ub, this);
if (!allbounded) {
r1.copyFrom(vars[v1]);
r2.copyFrom(vars[v2]);
IntIterableSetUtils.minus(r3, r1, r2);
change |= vars[vr].removeAllValuesBut(r3, this);
}
return change;
}
@Override
public ESat isEntailed() {
if (isCompletelyInstantiated()) {
return ESat.eval(vars[x].getValue() + vars[y].getValue() == vars[z].getValue());
}
return ESat.UNDEFINED;
}
@Override
public void explain(int p, ExplanationForSignedClause explanation) {
// super.explain(explanation, front, ig, p);
int m = explanation.readMask(p);
IntVar pivot = explanation.readVar(p);
IntIterableRangeSet dx, dy, dz;
if (IntEventType.isInclow(m)) {
if (pivot == vars[z]) {
int a = explanation.readDom(vars[x]).min();
int b = explanation.readDom(vars[y]).min();
dx = explanation.universe();
dx.removeBetween(a, IntIterableRangeSet.MAX);
dy = explanation.universe();
dy.removeBetween(b, IntIterableRangeSet.MAX);
vars[x].unionLit(dx, explanation);
vars[y].unionLit(dy, explanation);
vars[z].intersectLit(a + b, IntIterableRangeSet.MAX, explanation);
} else if (pivot == vars[x]) {
int a = explanation.readDom(vars[y]).max();
int b = explanation.readDom(vars[z]).min();
dy = explanation.universe();
dy.removeBetween(IntIterableRangeSet.MIN, a);
dz = explanation.universe();
dz.removeBetween(b, IntIterableRangeSet.MAX);
vars[x].intersectLit(b - a, IntIterableRangeSet.MAX, explanation);
vars[y].unionLit(dy, explanation);
vars[z].unionLit(dz, explanation);
} else {
int a = explanation.readDom(vars[x]).max();
int b = explanation.readDom(vars[z]).min();
dx = explanation.universe();
dx.removeBetween(IntIterableRangeSet.MIN, a);
dz = explanation.universe();
dz.removeBetween(b, IntIterableRangeSet.MAX);
vars[x].unionLit(dx, explanation);
vars[y].intersectLit(b - a, IntIterableRangeSet.MAX, explanation);
vars[z].unionLit(dz, explanation);
}
} else if (IntEventType.isDecupp(m)) {
if (pivot == vars[z]) {
int a = explanation.readDom(vars[x]).max();
int b = explanation.readDom(vars[y]).max();
dx = explanation.universe();
dx.removeBetween(IntIterableRangeSet.MIN, a);
dy = explanation.universe();
dy.removeBetween(IntIterableRangeSet.MIN, b);
vars[x].unionLit(dx, explanation);
vars[y].unionLit(dy, explanation);
vars[z].intersectLit(IntIterableRangeSet.MIN, a + b, explanation);
} else if (pivot == vars[x]) {
int a = explanation.readDom(vars[y]).min();
int b = explanation.readDom(vars[z]).max();
dy = explanation.universe();
dy.removeBetween(a, IntIterableRangeSet.MAX);
dz = explanation.universe();
dz.removeBetween(IntIterableRangeSet.MIN, b);
vars[x].intersectLit(IntIterableRangeSet.MIN, b - a, explanation);
vars[y].unionLit(dy, explanation);
vars[z].unionLit(dz, explanation);
} else {
int a = explanation.readDom(vars[x]).min();
int b = explanation.readDom(vars[z]).max();
dx = explanation.universe();
dx.removeBetween(a, IntIterableRangeSet.MAX);
dz = explanation.universe();
dz.removeBetween(IntIterableRangeSet.MIN, b);
vars[x].unionLit(dx, explanation);
vars[y].intersectLit(IntIterableRangeSet.MIN, b - a, explanation);
vars[z].unionLit(dz, explanation);
}
} else { // remove
assert IntEventType.isRemove(m);
Propagator.defaultExplain(this, p, explanation);
}
}
}